Teardrops n Tiny Travel Trailers

I finally moved from graph paper and pencil, to actual parts.
After sitting in cardboard cutouts and feeling my way around, I decided on a 10 ft long, 5 ft high, 56 inch wide. (New beetle diesel tow car set the width.)
Harbor Freight 1700 lb trailer. I did move the axle back and lowered it with an axle flip.

I started out thinking that I wanted sandwich walls, plywood bonded inside and out. (+ fiberglass?)
After many sleepless nights and reading this forum, I decided to go with foam panels and fiberglass.
Plan was 1.5 inch foam, but I found 3 inch, used roofing panels, 4X8, felt covered, with one really clean side. (Back side has minor imperfections.)

The price was right, so I will have R 18 insulation and a slightly smaller interior. I purchased 12 in all, (Looks like I could just glue them all together and hollow out the inside javascript:emoticon(':lol:') )

I am still trying to figure out haw many kerfs per inch on the inside of the curved roof panels to allow a (somewhat) smooth curve on the outside.

Is this just guesswork, and trial and error, or is there a rule of thumb on how much I need to allow the inside to collapse for a given curve?

Is this because it is a cyniade based foam ?
anever heard of this foam before but you do know the requires for death by burning super glue right.
<1 full minuet in a 3x3 x3 box for it to be effective.>

I found that on a scrap piece, using a blade with a wide kerf, and cutting 2 inches down, every 3/4 inch on the inside of the curve, the material will easily make a 24 inch radius. This is with no external cracking or visible break to the arc. The inside pieces come into full contact, making excess filler unnecessary.
I applied sheet material and paint, inside and out, just to see the outcome. I think that done full size with resin and fiberglass cloth it should look good with a minimal amount of filler.